The present invention relates to an improvement in an electromagnetic contactor means of the type having an arc runner for extinguishing an arc.
In general, an electromagnetic contactor means of the type to which the invention is directed is used for starting and stopping three-phase induction motors and the like. Such electromagnetic contactor means are provided with arc extinguishing means for extinguishing the arc created upon disengagement of the contacts. The repeated starting and stopping of electric motors particularly creates problems, as will be described hereafter. As the range of uses of such electromagnetic control means increases, e.g., to drive any automatic power-saving means and the like, there is a need for improvements in the arc extinguishing capabilities.
A conventional electromagnetic contactor means with a conventional arc runner is shown in FIGS. 1 through 4. In these drawings, reference numeral 1 denotes a mounting table made of an insulating material such as plastic or the like. Mounting table 1 is provided with a plurality of mounting holes 1a which are used to properly adjust the position of the electromagnetic contactor means. Reference numeral 2 denotes a base which is made of an insulating material. This base 2 is fixed by means of the mounting table 1 and a screw 3. Reference numeral 4 denotes a fixed iron core of laminated silicon steel plates. An operational coil 5 is mounted to the fixed iron core 4. In addition, there is interposed a flat spring 6 as a buffer material in the gap between it and the mounting table 1. Reference numeral 7 denotes a movable iron core which is arranged in such a way as to be opposite to the fixed iron core 4. If an electric current is passed through the operational coil 5, the moveable core 7 is pulled in such a way as to come in contact with the fixed iron core 4. Reference numeral 8 denotes a cross bar which is attached to the moveable iron core 7 via a pin 9. Reference numeral 10 denotes an unfastening spring which is disposed between the cross bar 8 and the mounting table 1. Usually, the unfastening spring 10 pushes the cross bar 8 so as to keep open the main circuit of the electromagnetic contactor means. Reference numeral 11 denotes a moveable contactor which is provided with a contact 11a. This moveable contact 11 is inserted into a retaining hole 8a which is formed in the cross bar 8, and a pressure is applied thereto by means of a pressure spring 12. Reference numeral 13 denotes a fixed contactor which is provided with a contact 13a opposite to the contact 11a of the moveable contactor 11. This fixed contactor 13 is fixed to the base 2 by means of a screw 14 and is provided with a terminal screw 15 to be connected to the electric wire of the main circuit. Reference numeral 16 denotes a cover made of an insulating material. This cover 16 is fixed to the base 2 by means of a screw 17.
Reference numeral 18 denotes an arc runner made of magnetic metal material which is formed in such a way as to surround the contact portion 11a of the moveable contactor 11 as well as the contact portion 13a of the fixed contactor 13. As shown in detail in FIG. 4, this arc runner 18 is bent in such a way as to have a cross-section of ]-shape. This arc runner is composed of a driving part 18a for driving the arc as well as an overhanging plate part 18b which covers the upper portion of the driving part 18a.
Now, the opening and closing operation of this electromagnetic contactor means will be explained. When a voltage is applied to the operational coil 5, a magnetic flux is produced in the gap between the fixed iron core 4 and the moveable iron core 7, and the moveable iron core 7 is pulled towards the fixed iron core 4 so as to be in contact therewith against the spring force of the unfastening spring 10. At this time, the cross bar 8 which is attached to the moveable iron core 7 is also actuated in the same way. The contact 11a of the moveable contactor 11 comes into contact with the contact 13a of the fixed contactor 13 and, at the same time, a predetermined pressure is applied thereto by means of the pressure spring 12 so as to close the main circuit.
In order to disconnect the main circuit, the operational coil 5 is demagnetized. The moveable iron core 7 moves away from the fixed iron core 4 due to the energizing force of the unfastening spring 10. The cross bar 8 also moves in association with the movement of moveable iron core 7. Therefore, cross bar 8 is returned to the position as shown in FIG. 2 and at the same time, contact 13a of the fixed contactor 13 disengages from the contact 11a of the moveable contactor 11.
During the disengaging of the contacts, an arc is generated at the portion indicated by (a) in FIG. 2 in the gap between the contact 11a and the contact 13a. This arc is driven by the driving part 18a of the arc runner 18 and moves to the position indicated by (b). Furthermore, as indicated by (c), this arc moves to the gap between the overhanging plate part 18b of the arc runner 18 and the movable contactor 11 and is extinguished.
A hot gas is generated along with the generation of the arc, and it flows out by way of the retaining hole 8a of the cross bar 8. As a result, the elasticity of the pressure spring 12 which is arranged in the retaining hole 8a is deteriorated, thereby resulting in a fused bonding between the contacts 11a and 13a. In addition, if the opening and closing operation of the electromagnetic contactor means is repeated frequently, a lot of hot gas is generated and the temperature of the arc runner, in particular, the overhanging plate 18b which is directly exposed to the arc, becomes abnormally high due to the insufficiency of the heat capacity of the arc runner 18. As a result, part 18b becomes curved and approaches the moveable contactor 11. As a consequence, further arcs are generated in the vicinity of the approaching part of 18b, thereby fusing and spoiling the moveable contactor 11. Furthermore, since the arc is not sufficiently long under the latter condition, the cooling effect is lowered and the shielding ability is reduced.